MNR, Canada's most powerful research reactor

The McMaster Nuclear Research Reactor (MNR), which began operation in April 1959, is located on the campus of MacMaster University in Hamilton, Ontario, Canada.

The MNR is the first university research reactor in the Commonwealth of Nations and Canada's largest neutron source.

It is a world leader in the production of iodine-125, a radioactive isotope used in the treatment of prostate cancer, and produces hundreds of doses each week.

It is a 5 MW open pool reactor consisting of two connected pools. The possibility that the core can be located and operated in either pool allows it to be moved away from the experimental apparatus for easy maintenance. It is fed with low-enriched uranium and cooled and moderated with light water. Heat is transported to the atmosphere through two cooling towers adjacent to the reactor building.

The MNR core is visible while the reactor is in operation. It appears to glow blue when viewed from the surface due to a process known as Cherenkov radiation. In the reactor pool, the radiation causes particles to travel faster than light can travel through water. These fast-moving particles excite electrons in the water molecules, which release energy in the form of photons or light, creating a blue glow.

The McMaster nuclear reactor performs hundreds of thousands of neutron irradiations each year, many in support of industry (mining exploration, environmental sampling).

As a curiosity, researchers using neutrons from the MNR discovered that a Van Gogh painting concealed one of his earlier compositions underneath, confirming the painter's well-known practice of recycling his canvases.

Although the MNR does not produce energy, the possibility of incorporating small modular reactors (SMRs) is being evaluated as a central part of Canada's Net Zero Plan to provide safe and affordable low-carbon energy.